1. Field of the Invention
The present invention relates to a fluid-insulated electrical apparatus in which an energization conductor is accommodated in a grounded tank filled with an insulating fluid such as gas or oil.
2. Description of the Related Art
A gas-insulated electrical apparatus is an example of an electrical apparatus that uses gas as an insulating medium. In a typical gas-insulated electrical apparatus, an energization conductor to which a high voltage is applied is placed inside a metal vessel. A gas insulated electrical apparatus is both highly reliable and stable because the metal vessel protects the energization conductor from any external factors and it is environmental-friendly as well.
However, there is a possibility that a foreign metal substance such as metal powder can invade the grounded tank in the process of assembling the gas insulated electrical apparatus. When a high voltage is applied to the energization conductor in a state in which a foreign metal substance exists inside the grounded tank, the foreign metal substance in the grounded tank moves up and down in a space between the grounded tank and the energization conductor at a cycle of several hertz (Hz). Presence of foreign metal substances in the grounded tank is not preferable in view of insulation of the gas insulated electrical apparatus, and it is one of the main factors that causes degradation of the withstanding voltage. A conventional apparatus that collects and traps foreign metal substances present in the grounded tank is described below.
Japanese Patent Application Laid-open No. S54-86737 discloses a conventional technique in which a conductor through which a high-voltage current flows is supported by an insulated spacer at the center of a grounded tank. This grounded tank is a pipe-shaped airtight metal vessel and it is filled with insulating gas. Moreover, a plurality of metallic materials is formed on a lower portion of an inner surface of the grounded tank in such a way that their inclined surfaces overlap each other. Each metallic material has a shape in which one end, which faces the energization conductor, is rounded, and the other end is fixed to the inner surface of the grounded tank.
After the gas insulated electrical apparatus is installed, a high voltage is applied between the conductor and the grounded tank in a normal use state. Any foreign metal substance that exists in the grounded tank gets electrically charged and begins to move, but any foreign metal substance that contacts the surface of any of the metallic materials falls along their inclined surfaces that overlap each other and is trapped in an area surrounded by the metallic materials. As a result, degradation of the withstanding voltage of the airtight gas insulated electrical apparatus can be prevented.
The conventional gas-insulated electrical apparatus has the following problems. In order to reduce the distortion of an electric field generated in the bottom of the grounded tank, the end of the metallic material that faces the energization conductor is rounded. However, an electric field is enhanced because of the rounding of the energization conductor, so that the electric field generated is distorted. As a result, the foreign metal substance reaches a portion of the head top portion in which the electric field is high, and as such, it becomes difficult to trap the foreign metal substance.